The new website is supposed to fix the scooping up issue by requiring the name of the person on each ticket. They can ask you for an id that matches the name on the ticket. This is what they say:
Parco archeologico del Colosseo nominative tickets
The Full Experience Underground and Arena tickets and the Moon over the Colosseum event tickets are nominative and show the personal data of the visitor. The nominative ticket will show the data of each group or family member.
In case of mismatch with the identity document, access to the Colosseum will not be allowed and no refund will be granted.
The tour operators using the B2B channel will be required to enter the name of the users of tickets at the time of purchase, with the possibility of changing it once only, no later than midnight of the third day prior to the date of use of the ticket.
Please also note that each operator may purchase a maximum of 500 tickets per day on the B2B channel.
Right now they are only selling tickets for up to one month from today. The guided tour tickets are sold out. The regular admission for "Individuals" (no guided tour) are available for every day and there are plenty of tickets available (€24). Tickets that include the underground are only available with a guided tour. All the "Full Experience" tickets (with or without a guided tour include admission to the Forum and Palatine Hill and all the SUPER sites.
It used to be that new tickets were released at midnight Rome time. I expect that is still the same.